Several proposals have been made to reduce the relatively high cost of producing the cases which are used in book binding. In approximately the last dozen years various proposals have been made for making book cases from plastic which permits them to be made in one piece and thus reduces the cost.
A principal difficulty in the manufacture of cased books using plastic cases is that the plastic materials having properties which make them most desirable for this purpose have surfaces to which the paper liners used in cased books cannot be adhered by means of animal glue or water base adhesives which are commonly used in book binding.
U.S. Pat. No. 3,088,753 relates to a plastic book cover of a non-stretchable synthetic polymer which is formed in a mold. The patent states in part
"A layer of paper 56 is shown bonded to the inside of each panel of the cover. This paper may be heat-sealed to the plastic cover by applying the paper while the plastic is still sticky in the mold. . . ." PA1 "If the paper 56 is not applied to the cover while the cover is still in a sticky condition in the mold, an adhesive must be used. Most adhesives are not suitable for this purpose. . . . Latex base adhesives have been satisfactory in practice, . . ."
U.S. Pat. No. 3,532,363 relates to bonding the rear edges of the pages of a book to the backbone of a plastic cover, and describes the use of an intermediate hot melt adhesive strip for this purpose, or alternatively a plastic material which is a good adhesive for paper.
Neither of the foregoing prior art patents discloses any way of adhering the end sheets of a book to the inner surfaces of plastic case front and back panels with the ordinary adhesives used in book binding; and in fact U.S. Pat. No. 3,088,753 states that such adhesives are not satisfactory for the purpose.